> All of which is an argument against the usefulness of the ER model's> many-to-many relationships idea. In this case, was the ER model> clearer without an explicit 'enrollement' entity?

FWIW,
I always go directly to the physical model. After all, the folks who
typically consume the model are developers. The businessness folks do
the 'sign-off' and they're easily 'trained' to read the physical
model. :)